Wireless communications systems are widely deployed to provide various types of communication content such as voice, video, packet data, messaging, broadcast, and so on. These systems may be multiple-access systems capable of supporting communication with multiple users by sharing the available system resources (e.g., time, frequency, and power). Examples of such multiple-access systems include code division multiple access (CDMA) systems, time division multiple access (TDMA) systems, frequency division multiple access (FDMA) systems, and orthogonal frequency division multiple access (OFDMA) systems, (e.g., an LTE system).
By way of example, a wireless multiple-access communications system may include a number of base stations, each simultaneously supporting communication for multiple communication devices, which may be otherwise known as user equipment (UEs), mobile devices or stations (STAs). A base station may communicate with the communication devices on downlink channels (e.g., for transmissions from a base station to a UE) and uplink channels (e.g., for transmissions from a UE to a base station).
In wireless communications systems, a transmitter (e.g. base station) may utilize multiple (NT) transmit antennas for data transmission to a receiver (e.g., communication device) equipped with multiple (NR) receive antennas. The multiple transmit and receive antennas form a multiple-input multiple-output (MIMO) channel that may be used to increase throughput and/or improve reliability. For example, the transmitter may transmit up to NT data streams concurrently from the NT transmit antennas to improve throughput. Alternatively, the transmitter may transmit a single data stream from all NT transmit antennas to improve reception by the receiver. Each data stream may carry one transport block or packet of data in a given transmission time interval.
In some aspects, good performance (e.g., high throughput) may be achieved by precoding one or more data streams with a precoding matrix selected based on the response of the MIMO channel from the transmitter to the receiver. Precoding may also be referred to as beamforming, spatial mapping, etc. However, in some aspects, a transmitter may limit the selection of a precoding matrices based on a precoding weight set restriction when a single stream transmission is selected by the transmitter. Restricting the use of one or more precoding matrices may result in performance degradation due to the limited flexibility imposed in beamforming for single stream transmissions.